1. Field of the Invention
This invention relates generally to a semiconductor wafer transport container. More particularly, this invention relates to a semiconductor wafer transport container having a semiconductor wafer cassette and semiconductor wafers enclosed therein; rotary retainers, integral with the container, retain semiconductor wafers within the semiconductor cassette during transportation and storage. The container allows the semiconductor wafer cassette and wafers to be removed from the container, wherein the likelihood of damaging the semiconductor wafers is decreased, without requiring manual manipulation of the container.
2. Discussion of the Related Art
The production of semiconductor wafers requires an extremely clean environment. When transporting and storing the semiconductor wafers, the presence of any small particles, vapors or static discharge in the environment is damaging to the production of the semiconductor wafers, and to the semiconductor wafers themselves. Hence, various techniques are in use today for transporting and storing semiconductor wafers in a particle free environment.
A semiconductor wafer cassette may be securely enclosed within a sealable box known as a WIP box. Semiconductor wafers are placed within the enclosed semiconductor wafer cassette. The semiconductor wafer cassette, the semiconductor wafers, and the inside of the WIP box must all be free of particles damaging to the semiconductor manufacturing process. During transportation of the WIP box, wafers and cassette, any movement of the semiconductor wafers or wafer cassette abrades the contacted surfaces. These abraded surfaces release particulate that is damaging to the wafers. Therefore, there is a need for a transport box which prevents the movement of the wafers within the box.
Also, during the transportation of semiconductor wafers enclosed within a WIP box, the wafers may be damaged from shock or jostling of the box. The jostling of wafers may also cause the release of particulate from abrasion between the wafers and the cassette. To prevent wafer damage and particulate release, the wafers must somehow be held securely within the wafer cassette. In the past, various cushions have been used to press against the wafers, thereby preventing wafer movement within the wafer cassette.
The Kos patent, U.S. Pat. No. 5,255,797, describes cushions that attach to the opposing, outside sidewall of a wafer cassette. The cushions are designed to manually rotate through a slot in the sidewall. Each cushion aligns and engages with a wafer within the cassette. The cushions move in a linear arcuate motion, pivoting around a mounting means that is attached to the cassette side walls. Each cushion of the Kos patent has a pivot pin which is a part of the mounting means. To move the cushions, the operator must manipulate the cushions manually, swinging the cushions through the slot in the cassette's sides.
The manual manipulation of the Kos' cushions requires additional steps to prepare the wafers for transportation and storage. Also, each cushion pivots independently, thereby increasing the surface area subject to abrasions. Hence, there is greater potential for a release of particulate during operation of these cushions. Further, the sidewall slots increases the potential that particulate will reach the semiconductor wafers, causing damage to the semiconductor wafers. Thus there is a need for a cushion that automatically retains the wafers within the cassette without increasing the amount of abraded particulate.
Other various transport containers include a box and door having cushions attached to the inside of the box wall. The cushions hold the semiconductor wafers within the semiconductor wafer cassette. When the box and door are engaged the cushions move inward towards the open end of a properly aligned wafer cassette. One such device was contemplated in the Maney et al patent, U.S. Pat. No. 4,815,912 (the '912 patent). The Maney '912 patent discloses a cushion that is attached to the inside of the box sidewalls by parallelogram arms. When the box and door are engaged, the parallelogram arms swing the cushion upward, towards the wafer. The cushions move in a simultaneously horizontal and vertical linear motion. A force perpendicular to the plane of the wafer is applied by the cushion, when the cushion contacts the wafer's profile edge. This force increases the potential for damage and breakage of the semiconductor wafers. The damage of semiconductor wafers can prove costly to the manufacture of semiconductor wafers. Hence there is a need for a cushion that does not retain the wafers by applying a force perpendicular to the plane of the wafer.
In the Maney transport container, disengaging the box and door causes the cushion to move away from the wafers. As the box is disengaged, a gravitational force moves the cushions away from the wafers. However, the box must be aligned vertically to effectuate the gravitational force. If the container is tilted, the gravitational force may not be sufficient to move the cushions. The fragile wafers are damaged when the cushions do not move completely away from the wafers. Also, depending on the flexibility of the parallelogram arms, gravity may not provide a sufficient force to effectively move the cushions away from the wafers. Further, the cushion may not move far enough away from the wafers to allow the box to be disengaged from the door without careful manipulation. Hence, there is a need for a cushion that automatically restrains the wafers when the box and door are engaged, without an increased likelihood of wafer damage or particulate release. There is a further need for a cushion which automatically retracts completely away from the wafer when the box and door are disengaged.
The present invention overcomes the disadvantages of the current devices by providing a plurality of wafer retaining fingers or cushions that automatically rotate, simultaneously, into contact with the wafers when the box is engaged with the door. The automatic rotational movement, rather than linear motion, sufficiently removes the fingers away from the wafers, when the box and door are disengaged. Also, the present invention is more efficient requiring less manual manipulation. Further, each wafer retaining finger is designed to reduce the amount of abrasion from contact while still holding the wafer in place. Also, the fingers apply a force parallel to the planar surface of the wafers, thereby reducing the risk of damage to the wafers.